Conventionally, as a method for forming a foundation pile of buildings and the like, it is well-known a method for burying a precast pile. Further, as the method for burying a precast pile, it is well-known a pre-boring piling method in which construction is conducted to loosen the ground before burying the precast pile in the underground and a hollow drilling construction method in which the pile is buried while drilling the underground around a top portion of the pile and discharging soil by utilizing a hollow portion of the pile.
First, in the pre-boring piling method, a borehole is constructed at an extent of a predetermined depth while ejecting water for drilling from a top portion of a drill bit in an excavator. Next, the drill bit is repeatedly moved in up and down direction while injecting root consolidation solution in the top portion of the borehole, thereby soil cement is formed by stirring and mixing mud and the root consolidation solution. Further, after the drill bit is pulled out from the borehole, the precast pile is built in the borehole before the soil cement is hardened and the top of the precast pile is settled in the soil cement for root consolidation.
In the other hollow drilling construction method, drilling operation of the ground by the excavator and sinking of the pile are conducted at the same time and such piling method is almost same as the pre-boring piling method in a construction method of the root consolidation portion in which construction is conducted by injecting the root consolidation solution in the borehole.
Using these two kinds of methods, a root consolidation portion is formed at the top portion of the pile by generally filling the cement milk in which cement and water are mixed in the borehole as the root consolidation solution and hardening the cement milk, thereby it is formed construction hardening the supporting ground. Water cement ratio in the cement milk of the supporting pile generally used is usually from 55% to 65% and strength of age for 28 days is controlled to an extent of from 11 to 20 N/mm2.
In the pre-boring piling method, based on an object to integrate a surrounding of the precast pile built in the borehole and a surrounding wall surface of the borehole, the cement milk which has the water cement ratio equal to or greater than that of the root consolidation solution is made into the soil cement obtained by stirring with the drilled soil and the pile surrounding consolidation solution controlled so that the strength of age for 28 days becomes more than 0.5 N/mm2 is filled.
Further, concerning the pile consolidation solution as the root consolidation solution or the pile surrounding consolidation solution, it is well-known various kinds of solutions such as solution in which expanding material is added to the injected cement milk or in which blast furnace slag mixed cement is utilized in the cement milk or in which blast furnace slag cement class B is made main material in the cement milk or in which plaster is utilized. It is disclosed in the following patent literatures a method to increase tip support force of the precast pile by utilizing above solutions.
In the Patent Literature 1, it is disclosed a technology that the root consolidation solution prepared so that expanding agent 4.5˜11% of calcium sulfoaluminate type is added to cement paste and water cement ratio against total of cement and expanding agent is made lower than 65%, is expanded in a bulb hardening process, thereby the bulb is pressurized to contact with the ground. According to the technology disclosed in the Patent Literature 1, uniaxial constraint expansion coefficient becomes 45×10−4 (4500×10−6) at maximum, thus maximum expansion coefficient becomes to an extent of 4.5%.
Further, in the Patent Literature 2, it is disclosed a technology that the pile surrounding consolidation solution composed of cement in which blast furnace slag fine powder is mixed, water, fine aggregate, anhydrous plaster, thickener, water reducing agent, is filled in pile surrounding of the borehole, thereby adhesion between the pile and the ground is improved. According to the technology disclosed in the Patent Literature 2, since change in length of expansion is made valid until 6000×10−6, the maximum expansion coefficient becomes 0.6%.
Furthermore, in the Patent Literature 3, it is disclosed a pile surrounding filling solution mainly composed of blast furnace cement class B and binder including anhydrous plaster and water. According to the technology disclosed in the Patent Literature 3, since expansion amount is made to the extent of 2500 μm (2500×10−6) more than 1200 μm (1200×10−6), the maximum expansion coefficient becomes 0.25%.